When a conductive layer of a semiconductor device is recessed, batch wet etching may be performed with mixed acid that contains phosphoric acid, acetic acid and nitric acid. However, it is difficult to circulate the mixed acid even if it is heated at high temperature since the viscosity of phosphoric acid is high. Therefore, the acetic acid is added in the mixed acid to reduce the viscosity of the mixed acid. However, when the mixed acid is heated at high temperature to be circulated, the acetic acid is evaporated from the mixed acid during the circulation of the mixed acid. As a result, the viscosity of the mixed acid increases, which causes problems that in-plane uniformity of a recess amount of the conductive layer deteriorates and a circulating flow rate error of the mixed acid is liable to arise.